In the analogue domain of cellular networks, filtering of various types is often required. For example, in the uplink part of some radio base stations, certain frequency sub bands are filtered out and shifted to new centre frequencies. This allows frequency domain multiplexing to reduce the number of cables required between antennas and the main part of the radio base station.
The frequency band varies in extent and position depending on radio technology used and/or allocations of frequencies for a particular operator. It would be beneficial if there were a filter apparatus which is configurable both in bandwidth of the desired signal and centre frequency for the output signal.
U.S. Pat. No. 5,987,304 presents a mobile telephone repeater with a variable bandwidth. The repeater comprises an uplink and downlink, each being provided with amplifier chains. Each chain comprises at least two band pass filter units coupled in series and having controllable pass bands, which at least partially overlap each other. The center frequency of the filter units are controllable so as to make the bandwidth of the resulting pass band variable. Consequently, the effective bandwidth of the amplifier chain is controllable. However, it would be beneficial if greater flexibility in configuration is achieved, preferably also with fewer components.